C-Sharp Silverlight

How to Efficiently Update Your UI While Uploading Files in Silverlight Using `HttpWebRequest`

When working with file uploads in Silverlight using HttpWebRequest, developers often encounter a significant challenge: updating the UI in real-time while the files are being uploaded. This process can lead to UI freezing or deadlocks, particularly when attempting to interact with UI elements from an asynchronous callback. In this blog post, we’ll explore this problem in detail and discuss a reliable solution to ensure a smooth user experience without sacrificing application performance.

Understanding the Problem

The Scenario

You may find yourself in a situation where you’re uploading multiple files and wish to inform the user about the upload progress. This involves actively updating a progress bar or similar UI component while the data stream is being processed. Here’s a simplified example of what can go wrong:

When you call Dispatcher.BeginInvoke inside the upload loop, the UI may freeze, leading to a poor user experience. As the UI is running in a single thread, any long-running operations can block it, effectively causing your application to appear unresponsive.

The Deadlock Dilemma

When performing file uploads, if the UI thread is busy waiting for uploads to complete, the application’s responsiveness deteriorates, making it seem like the browser or the application is stuck. This scenario is particularly common in Silverlight applications where running asynchronous operations can lead to thread management issues, hence resulting in deadlocks.

The Solution: Using `AllowReadStreamBuffering`

One effective way to address this issue is to configure the HttpWebRequest by setting the AllowReadStreamBuffering property to false. This change allows for streaming data without blocking the request, enabling you to update your UI while the upload is in progress. Here’s how to implement this solution:

Step-by-Step Implementation

Set Up the HttpWebRequest: Ensure your request allows for streaming by modifying the properties as follows:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(ub.Uri);
request.Method = "POST";
request.AllowReadStreamBuffering = false;  // Enable streaming

Modify UI Update Logic:
- Ensure that the UI updates are managed in a way that doesn’t block the application’s main thread.
- Consider implementing progress updates in a way that minimizes the number of calls to Dispatcher.BeginInvoke.
Example:
```
// Inside the PushData method
if (bytesReadTotal % BUFFER_UPDATE_INTERVAL == 0)
{
    Dispatcher.BeginInvoke(() =>
    {
        this.ProgressBarWithPercentage.Percentage = totalPercentage;
    });
}
```
Here, BUFFER_UPDATE_INTERVAL can be a set value that controls how often the UI is updated, reducing the call frequency and improving performance.

Additional Tips

Chunking Data: Break large files into smaller chunks during the upload process. This method not only ensures a smoother UI experience but also allows for better management of upload failures and retries.
Testing and Debugging: Implement extensive testing under various user scenarios to identify any potential performance issues related to UI freezing or application deadlocking.

Useful Resources

Conclusion

By configuring HttpWebRequest to allow streaming and optimizing how UI updates occur, developers can significantly enhance user experiences in Silverlight applications during file uploads. Remember, the key is not only to facilitate data transmission but also to maintain a responsive UX. Implement the steps shared in this blog, and say goodbye to the frustrations of unresponsive applications!

How to Efficiently Update Your UI While Uploading Files in Silverlight Using HttpWebRequest